1. Technical Field
The present invention relates to a cavity-backed microstrip dipole antenna array, and more particularly, to a low profile cavity-backed microstrip dipole antenna array capable of forming a precise beam and transmitting or receiving linearly polarized waves over a relatively wide bandwidth.
2. Related Art
Generally, microstrip or patch dipole antennas have been used for years as compact radiators of electromagnetic radiation. The antennas are designed in an array and may be used for communication systems such as identification of friend or foe (IFF) systems, personal communication service (PCS) systems, and satellite communication systems, which require characteristics of low cost, light weight, low profile, a precise form of beam and a low sidelobe.
A conventional microstrip patch antenna array having radiators and feeders which are etched on a single printed circuit board (PCB), such as disclosed in U.S. Pat. No. 3,995,277 for Microstip Antenna issued to Olyphant, Jr., U.S. Pat. No. 4,575,725 for Double Tuned, Coupled Microstrip Antenna issued to Tresselt, and U.S. Pat. No. 4,740,793 for Antenna Elements And Arrays issued to Wolfson et al., is low cost, lightweight and low profile. However, the microstrip path antenna usually operates over a narrow frequency bandwidth of 1.about.5% of the center frequency.
An inverted patch antenna array of a strip-slot form, and a stacked patch antenna array, as disclosed, for example, in "Broad Band Patch Antenna" written by J. F. Zurcher and F. E. Gardiol, 1995, Artech House, U.S. Pat. No. 5,300,936 for Multiple Band Antenna issued to Izadian, U.S. Pat. No. 5,400,042 for Dual Frequency, Dual Polarized Multi-Layered Microstrip Slot And Dipole Array Antenna issued to Tulintseff, U.S. Pat. No. 5,661,493 for Layered Dual Frequency Antenna Array issued to Uher et al., operate over a broader frequency bandwidth of, for example, 15.about.20% of the center frequency. However, at least two or three printed circuit boards (PCB) are required, which attribute to the high cost and the thickness of the array. In addition, the mutual coupling prevents the array from synthesizing a precise radiating pattern, for example, a low sidelobe or cosecant beam synthesis, and from minimizing undesirable cross polarizations. The same problems are also found in planar antenna arrays having window radiators as disclosed, for example, in U.S. Pat. No. 4,761,654 for Electromagnetically Coupled Microstrip Antennas Having Feeding Patches Capacitively Coupled To Feedlines issued to Zaghloul, U.S. Pat. No. 4,922,263 for Plate Antenna With Double Crossed Polarizations issued to Dubost et al., and U.S. Pat. No. 5,321,411 for Planar Antenna For Linearly Polarized Waves issued to Tsukamoto et al.
A conventional radiator most appropriate for suppressing the mutual coupling, improving polarization properties, and reducing edge effect and back radiation, is known as a cavity-backed radiator, as disclosed, for example, in "Microwave cavity antennas" written by A. Kumar & H. D. Hristov, 1989, chapter 1, and IEEE Antenna and Propagation Magazine, v.38, No. 4, 1966, pp. 7-12. A typical cavity-backed microstrip dipole array requires formation of multiple-beam and control of sidelobe, and is widely used for complex communication systems such as communication satellites "Odyssey". However, in the conventional cavity-backed array, the cavity has a depth of 0.3.about.0.6 times wavelength of the transmitted/received signal, and is located under a feeder network, which increases the thickness of the array. In addition, advanced printed circuit technology, which employs microstrip dipoles having a wide bandwidth and a strip line feeder network, is used for the formation of the cavity-backed microstrip dipole antenna as disclosed, for example, in U.S. Pat. No. 4,287,518 For Cavity-Backed, Micro-Strip Dipole Antenna array issued to Ellis, Jr. The cavity of the cavity-backed microstrip dipole antenna also requires a depth of approximately 0.3 times wavelength of the transmitted/received signal. Accordingly, the antenna cannot be thin. Moreover, a plurality of printed circuit boards (PCBs) for dipoles and a feeder network are necessarily used, which increase the cost of the array. Further, orthogonal junctions between a stripline feeder network and striplines of the dipoles require soldering and complicated fabrication techniques, which also attribute to the higher cost of the antenna array.